The use of fibrous materials as absorbents for moisture is a well known, widespread practice. In this application many of the natural and synthetic fibers have been used and extensive efforts have been made to improve the absorption properties of the materials. One of the major deficiencies of the natural and synthetic materials heretofore used has been the tendency for them to release the absorbed moisture when pressure has been applied to the moisture containing material. The fact that pressure causes the absorbed fluid to be expelled from the fibers is known as reversible absorption. For many applications, however, irreversible absorption is desired, for example, in surgical dressings, diapers, bed pads, catamenials, and the like, whereby the absorbed moisture is retained in the absorbent material under an applied pressure.
Within the past few years recent innovations have resulted in the production of materials having such irreversible absorption properties; these materials are now known as hydrogels. In most instances they have been produced in powder or particulate form and even, in some instances, in film form. An especially interesting characteristic of the hydrogel polymers is that when in contact with water they absorb it and swell to a certain point and stop and the final swollen polymer is still similar in shape to its initial unswollen shape. Many of the hydrogels have the ability to absorb many times their original weight in water without becoming soggy or deformed. In general, the hydrogels are used in conjunction with other materials as supports. Among the United States patents that have issued in this field are U.S. Pat. Nos. 3,669,103; 3,589,364; 3,694,301; 3,670,732; 3,164,565. This is but an exemplary listing and should not be considered complete. In addition, there are U.S. Pat. Nos. 3,939,105, 3,939,123 and 3,940,542 which are concerned with the polyurethane hydrogels whose wetting rates were still not completely satisfactory for some applications.